Geology topics

Laura Lalemand

Publications and source records attributed to Laura Lalemand.

3 recordsLinked to original sources

USGS2017

Higher sensitivity and lower specificity in post-fire mortality model validation of 11 western US tree species

Managers require accurate models to predict post-fire tree mortality to plan prescribed fire treatments and examine their effectiveness. Here we assess the performance of a common post-fire tree mortality model with an independent dataset of 11 tree species from 13 National Park Service units in the western USA. Overall model discrimination was generally strong, but performance varied considerably among species and sites. The model tended to have higher sensitivity (proportion of correctly classified dead trees) and lower specificity (proportion of correctly classified live trees) for many species, indicating an overestimation of mortality. Variation in model accuracy (percentage of live and dead trees correctly classified) among species was not related to sample size or percentage observed mortality. However, we observed a positive relationship between specificity and a species-specific bark thickness multiplier, indicating that overestimation was more common in thin-barked species. Accuracy was also quite low for thinner bark classes (<1 cm) for many species, leading to poorer model performance. Our results indicate that a common post-fire mortality model generally performs well across a range of species and sites; however, some thin-barked species and size classes would benefit from further refinement to improve model specificity.

International Journal of Wildland Fire↗

USGS2017

Growth of coast redwood and Douglas-fir following thinning in second-growth forests at Redwood National Park and Headwaters Forest Reserve

Managers of second-growth forests at Redwood National Park and the Bureau of Land Management’s Headwaters Forest Reserve encourage the development of late seral forest characteristics using mechanical thinning, where competing vegetation is removed to promote growth of residual trees. Yet the ability to quantify and reliably predict outcomes of treatments such as these is hindered by the long time scales at which forests respond to thinning. Here we present analyses of tree growth at Redwood National Park (RNP) and Headwaters Forest Reserve (HDWT) from sites that have had > 5 years to respond to thinning treatments. Compared to untreated stands, thinned stands had lower stem density (trees ha -1 ) and basal area (m 2 ha -1 ), primarily due to removal of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco). Individual tree growth (basal area increment, BAI, m 2 yr -1 ) was related to tree size (basal area, m 2 ) and treatment history, with the highest growth rates observed in large trees. Both redwood ( Sequoia sempervirens (D. Don) Endl.) and Douglas-fir appeared to have a small, but detectable, positive growth response to thinning treatments. Early results suggest a large degree of variation among sites, with possible systematic differences in growth responses between RNP and HDWT. Future work will focus on identifying site-level differences (site quality, local competition, slope, aspect, stand age, distance from the ocean) to improve our understanding of the growth response.

Redwood National Park and Headwaters Forest Reserv↗

USGS2016

Duration of fuels reduction following prescribed fire in coniferous forests of U.S. national parks in California and the Colorado Plateau

Prescribed fire is a widely used forest management tool, yet the long-term effectiveness of prescribed fire in reducing fuels and fire hazards in many vegetation types is not well documented. We assessed the magnitude and duration of reductions in surface fuels and modeled fire hazards in coniferous forests across nine U.S. national parks in California and the Colorado Plateau. We used observations from a prescribed fire effects monitoring program that feature standard forest and surface fuels inventories conducted pre-fire, immediately following an initial (first-entry) prescribed fire and at varying intervals up to >20 years post-fire. A subset of these plots was subjected to prescribed fire again (second-entry) with continued monitoring. Prescribed fire effects were highly variable among plots, but we found on average first-entry fires resulted in a significant post-fire reduction in surface fuels, with litter and duff fuels not returning to pre-fire levels over the length of our observations. Fine and coarse woody fuels often took a decade or longer to return to pre-fire levels. For second-entry fires we found continued fuels reductions, without strong evidence of fuel loads returning to levels observed immediately prior to second-entry fire. Following both first- and second-entry fire there were increases in estimated canopy base heights, along with reductions in estimated canopy bulk density and modeled flame lengths. We did not find evidence of return to pre-fire conditions during our observation intervals for these measures of fire hazard. Our results show that prescribed fire can be a valuable tool to reduce fire hazards and, depending on forest conditions and the measurement used, reductions in fire hazard can last for decades. Second-entry prescribed fire appeared to reinforce the reduction in fuels and fire hazard from first-entry fires.

Forest Ecology and Management↗